Conventionally, iron-based materials have been used in a wide range of fields because the iron-based materials are more excellent in mechanical properties, such as ductility, malleability, and tensile strength, and also in workability, as compared with other metallic materials. In the iron-based material, a steel structure or a cast iron structure can be obtained by adjusting the carbon content according to the use of the material.
For example, the steel structure can be obtained by making carbon contained in pure iron material in the range of 0.03% by mass or more to less than 1.7% by mass. The material having the steel structure is generally referred to as carbon steel. The material (steel material) having such steel structure is excellent in ductility, malleability, and workability, and hence is used for applications such as those for structures, machine components, and tools.
Further, in order to improve abrasion resistance and fatigue resistance, the steel material may be subjected to carburizing treatment which makes carbon solid-dissolved and diffused from the surface of the steel material within the above described range by heating the surface of the steel material in a predetermined temperature atmosphere together with a solid carburizing agent, such as corks, or a gas carburizing agent such as hydrocarbon-based gas. By performing the carburizing treatment, a layer made of a carburized structure is formed in the surface of the steel material.
On the other hand, the cast iron structure can be obtained by making carbon contained in pure iron material in the range of 1.7% to 6.68% by mass. Practically, in many cases, the cast iron structure contains carbon in the range of 2.5% to 4.5% by mass, and further contains silicon, manganese, phosphorus, sulfur, and the like. The cast iron structure is inferior in ductility and malleability as compared with the steel structure. However, the cast iron structure has a large compressive strength and is excellent in machinability, abrasion resistance, and impact absorbing property (vibration damping property).
For example, a disk rotor made of cast iron is proposed as a member using a east iron material (see patent document 1). The disk rotor is a disk-like component which configures a disk brake of a vehicle, such as an automobile. The braking surface of the disk rotor, against which surface a brake pad is pressed, is made of flake graphite cast iron. Since the cast iron material is excellent in abrasion resistance and impact absorbing property as described above, the braking surface of the disk rotor is hardly worn out and is able to absorb the vibration at the time of braking. Thus, according to such disk rotor, it is possible to suitably brake the vehicle.    Patent Document 1: JP Patent Publication (Kokai) No. 62-146280A (1987)